Cardiac pacing is used for clinical treatment and therapy of a patient and involves electrical cardiac stimulation to treat a tachyarrhythmia or bradyarrythmia. The pacing re-establishes circulatory integrity and normal hemodynamics that are compromised by a slow or fast heart rate by restoring an appropriate heart rate. Cardiac pacing may be lifesaving. Cardiac response signal analyses based on electrophysiological activity (such as surface ECG signals and ICEG (intra-cardiac electrograms)) and time domain parameters of the waveforms are utilized for cardiac arrhythmia detection and diagnosis, such as of P wave associated disorders like atrial fibrillation (AF) and ST segment changes for myocardial ischemia and infarction. However during heart pacing or stimulation, the cardiac electrophysiology responses (such as signal morphology, latency) are different from cases in a non-pacing situation. Known systems using P wave analysis methods, for example, typically fail to efficiently interpret and characterize cardiac signals during pacing. Furthermore, noise and artifact effects during pacing may be higher which may distort a cardiac electrophysiological signal, resulting in a false positive alarm, especially in ICD (implantable cardioverter-defibrillator) patients.
Early cardiac arrhythmia and pathology recognition, such as of atrial fibrillation, myocardial ischemia or infarction, and ventricle tachycardia, is desirable for rhythm management of cardiac disorders and irregularities. Known waveform morphologies and time domain parameter analysis of depolarization and repolarization functions, such as of a P wave, QRS complex, ST segment, T wave, are used for cardiac arrhythmia monitoring and identification. Known systems typically use RR wave detection to synchronize signal interpretation beat to beat. However RR wave detection may not be accurate during pacing or during electrical stimulation, especially for excitation time tracking and detection of signal morphology variation. Additionally unsuccessful pacing heart beats may cause variation (as well as unnecessary alarms or warnings) in signal evaluation and calculation. Furthermore, there may be substantial heart electrophysiological characteristic changes: such as absence of a P wave in the pacing signals and detection of an ST segment exceeding a 0.1 mV threshold (as typically used for cardiac condition detection) may not work for ischemia detection in pacing (especially for intra-cardiac electrograms (ICEG)). Also substantial signal magnitude shift, distortion or variation may occur in the presence of pacing.
Further known clinical methods for cardiac arrhythmia identification and analysis based on ECG signals are subjective and need extensive expertise and clinical experience for accurate interpretation and appropriate cardiac rhythm management. Improved objective analysis and diagnosis of cardiac signals and activities is desirable. Known methods based on RR wave detection may indicate unnecessary time variation for cardiac signal morphology analysis and therefore may be inaccurate in cardiac function evaluation and pathology diagnosis and known methods based on detecting amplitude (voltage) changes and variation may not be accurate for cardiac function evaluation and pathology diagnosis. Known pacing cardiac signals analysis is typically subjective and needs extensive physician pacing analysis experience and may be not be able to qualitatively and quantitatively capture or characterize signal changes, and predict a pathological trend, especially a real time growing trend of a cardiac arrhythmia, such as a pathology trend from low risk to medium, and then to high risk (severe and fatal) rhythm (especially in VT growing arrhythmia, for example).
Known excitation analysis typically involves tune stamping an R wave transition along myocardial tissue (such as by using different leads in a catheter coupled to different portions of cardiac tissue) but lack accurate methods to measure time duration and variation of signals from individual cardiac tissue portions. Absolute time synchronization variation may be used to detect local malfunctioning cardiac tissue, such as from a pacing spike to R wave, pacing spike to Q or S wave, but this may not work when patient pacing occurs. In known clinical applications, pacing energy and rate determination are typically physician controlled based on experience and therefore prone to human error. A system according to invention principles addresses these deficiencies and related problems.